Premium seats for civil aircraft have various seat positions, from the most upright to a full flat or lie flat bed position, especially for long or overseas flights. It is desirable to provide premium seats that allow such flexibility in seat movement, but that also provide as much space as possible for the passenger in each desired position.
Additionally, passenger vehicle seats need to be designed in order to provide easy access to passengers, particularly disabled passengers. For that reason, aisle side armrest are usually either removable, droppable, or rotatable in order to allow a passenger to be translated laterally from a wheel chair to the seat (or to otherwise provide increased access to the seats).